This invention relates to a microprocessor device and system, and more particularly to a microprocessor device containing integrated CPU, RAM, timer and bus arbiter for use in an adapter for coupling a host processor to a data communications loop.
The token-ring local area network is a data communications system functioning to transfer data among a number of stations coupled to a one-way signal path. Each station has a host processor with memory and various peripheral devices to function as an independent workstation. Access to the ring is controlled by token passing wherein a free or busy token is passed from one station to the next around the ring. An early example of the token ring is shown in U.S. Pat. No. 3,597,549 issued to Farmer & Newhall and assigned to Bell Telephone Laboratories. In further refinement, the so-called Munich ring has evolved from developments by IBM, reported at Proceedings of the National Telecommunications Conference November 1981, pp. A.2.2.1-A.2.2.6. Standard protocols for these communications methods have been published by the IEEE as the 802.5 token ring proposal, and a similar report by the European Computer Manufacturers organization.
The present invention is concerned with a microprocesor device used in an adapter for connection between the host processor and the signal path of the ring. The adapter must operate relatively independent of the CPU of the host processor so that a minimum of interference with the functions of the host CPU is needed. The adapter must accomodate a variety of different types of host CPU, so that a special adapter need not be manufactured for each different type of construction of the workstations. It is expected that entire office buildings or manufacturing facilities will be permanently wired to implement loop communications of this type between all computer terminals, word processors, telephones, bulk data storage stations, and the like. Thus, the adapters must be of relatively low cost, must be reliable and require little maintenance, must be of small size and dissipate little power, and above all must interface with a variety of differing systems.
It is the principal object of this invention to provide an improved microprocessor device for use in a data communications system, particularly in a communications adapter for coupling a host processor system to a token passing communications loop. Another object is to provide a communications adapter which has processing and control facility independent of the host system, and which operates with a variety of different host systems. A further object is to provide a low cost, low power, reliable and versitile microprocessor device for a communications adapter for token ring local area network systems or the like.